In the field of therapeutic fluid delivery, various approaches to instrumentation for controlling the infusion rate have been proposed. Some of the instrumentation previously disclosed utilizes a metering chamber divided into two compartments by a movable membrane. For example, U.S. patent application Ser. No. 404,811, filed Aug. 3, 1982, and owned by the owner of the present application, describes in detail a number of such systems for achieving volumetric accuracy of delivery. That application discloses a disposable cassette containing a dual chamber, with each compartment of the chamber being provided with a valved inlet and outlet. Upon opening of a valve pair comprising an inlet and an outlet on opposite sides of the membrane separating the two compartments, exactly one chamber's volume of fluid is delivered to the patient, and then fluid flow stops. The alternation of opening and closing of the two pairs of valves thus provides a digitized flow of fluid in precise volumetric quantities. By selecting the rate at which the valve states are initiated, the user may provide for the precise desired overall volumetric flow rate.
As can be seen from that application, the disposable cassette which carries the metering chamber and the four valves associated with the chamber must cooperate with an actuator for effecting the valve movement. Such an actuator, several examples of which are given in the application, serves as the mechanical interface between the microprocessor or other control intelligence which generates the timed control signals to achieve the desired volumetric flow rate, and the valves of the disposable cassette which actually serve to gate the fluid flow through the cassette. The invention of this application is directed to improvements in such mechanical interfaces.
Patent art of interest in the general field of fluid flow control utilizing chambers having a movable membrane may be found in U.S. Pat. Nos. 4,204,538, 4,207,871, 4,121,584, and in U.K. patent application Ser. No. 2,043,594 (published Oct. 8, 1980).